1. Field of the Invention
The invention relates to a pickup device for writing information to an information recording medium or reading information from the information recording medium and an information recording/reproducing apparatus having the pickup device.
2. Description of Related Art
In recent years, phase change type information recording media have been developed as information recording media of a large capacity which allows the recording of information at high density. The known kinds of the phase change type recording media are: a read only optical disc; a WORM-type optical disc in which information can be recorded once; and a rewritable type optical disc in which erasure and rerecording of information can be performed.
Those phase change type information recording media have a structure that information is recorded by causing a phase change of a crystal or amorphous recording layer or the like by means of light energy. The read only optical disc and WORM-type optical disc have such a characteristic that information is recorded only once by using its recording layer which is irreversibly changed by a light energy. The rewritable type optical disc has such a characteristic that information can be rewritten by using its recording layer which is reversibly changed by light energy. According to those phase change information recording media, the high density recording of information can be performed by narrowing the so called track pitch.
To realize an information recording/reproducing apparatus adapted to the information recording media that can perform the high density recording, there considered is a method for increasing a numerical aperture (NA) of an objective lens provided in the so-called pickup device, thereby a laser beam of a small irradiation diameter is irradiated to the recording layer. Thus, high density recording of information or reproduction of the information recorded at high density is performed.
It is also considered to apply a crosstalk cancelling technique in order to perform a precise reproduction of information in a limited range of the numerical aperture NA of the objective lens.
In the case of the reproduction of information from the phase change type information recording medium by using the conventional crosstalk cancelling technique, however, there are the following problems.
First, according to the conventional crosstalk cancelling technique, different laser beams are simultaneously irradiated to both of a track on which information to be reproduced has been recorded (hereinafter, referred to as a main track) and tracks adjacent to the main track (hereinafter, referred to as adjacent tracks), the reflection light by the laser beam irradiated to the main track (hereinafter, referred to as a main beam) and the reflection light by the laser beams irradiated to the adjacent tracks (hereinafter, referred to as sub beams) are optically detected, and a predetermined arithmetic operating process is performed based on each of detection signals detected, thereby removing a crosstalk component included in the detection signal reproduced from the main track.
In the conventional pickup device, an optical system having such a structure that an objective lens is used commonly for the recording of information and the reproduction of information in order to realize miniaturization, reduction of the weight, or the like. More specifically, there used is a construction such that a light emitted from a laser light source provided for the optical system is divided into a 0th order light beam and xc2x11 primary light beams by means of a grating (diffraction grating), the 0th order light beam is irradiated as a main beam to the main track through the objective lens, and the xc2x11 primary light beams are irradiated as sub beams to the adjacent tracks through the objective lens. That is, according to the conventional pickup device, the main beam and the sub beams are irradiated in each of the recording of information and the reproduction of information.
Therefore, if the power of a laser light source is raised in order to raise the power of the main beam (0th order light) to record information to the WORM-type optical disc or rewritable type optical disc, the powers of the sub beams (xc2x11 primary light) are also raised accordingly. A problem is that, upon recording of information, the information already recorded on the adjacent tracks is erased or destroyed by the sub beams of the high powers, consequently.
To avoid the problem associated with the recording of information mentioned above, a method of reducing the powers of the sub beams (xc2x11 primary light) by using a grating of a low diffraction efficiency has been considered. In this case, however, the power of the main beam (0th order light) rises by an amount corresponding to the reduced amount of the powers of the sub beams (xc2x11 primary light) due to the use of the grating. Therefore, if the main beam and the sub beams are irradiated in order to effect the crosstalk cancellation when the information is reproduced from the read only optical disc, WORM-type optical disc, or rewritable type optical disc, a problem arises that the information on the main track is erased or destroyed by the high power main beam although the erasure or breakage of the information on the adjacent tracks by the sub beams is avoided.
The invention has been made to solve the problems of the conventional arrangement mentioned above, and it is an object of the invention to provide a pickup device and an information recording/reproducing apparatus, which allows execution of a precise recording of information to an information recording medium to which high density recording can be performed and a precise reproduction of information from the information recording medium to which the information has been recorded at high density.
Another object of the invention is to provide a pickup device which enables the recording of information and the reproduction of information to be performed by a same objective lens even when the crosstalk cancelling technique is applied.
According to a first aspect of the invention, there is provided a pickup device for recording information to an information recording medium and/or reproducing information from the information recording medium, comprising: a light source for emitting first light for irradiating a first laser beam for recording information or reproducing information onto the information recording medium at the time of the recording of information or the reproduction of information and second light for irradiating a second laser beam onto a track adjacent to a track on which the first laser beam is irradiated at least at the time of the reproduction of information; and control means for independently controlling powers of the first light and the second light.
According to the pickup device with this construction, by properly controlling the powers of the first light and the second light, the powers of the first light and the second light which are irradiated to the track of the information recording medium at the time of the recording of information or reproduction of information are adjusted, so that erasure or the like of the information which has already been recorded on the track can be prevented. At the time of the reproduction of information, each reflection light which is caused when the first and second laser beams are reflected by the track is detected and information in which crosstalk components have been suppressed can be reproduced on the basis of detection results.
According to the second aspect of the invention, the pickup device further has a grating arranged between the light source and the information recording medium, the light source has a structure such that the first and second lights whose polarizing directions cross perpendicularly are emitted, and the grating has a structure such that the first light is transmitted without being diffracted and the second light is diffracted and transmitted.
According to the pickup device with this construction, by adjusting a diffraction efficiency of the grating, the first and second laser beams with powers such that the information which has already been recorded on the track is not erased or the like at the time of the recording of information or reproduction of information can be formed.
According to the third aspect of the invention, in the pickup device according to the second aspect of the invention, the light source further has a single semiconductor laser or different semiconductor lasers for emitting the first and second lights whose polarizing directions cross almost perpendicularly.
According to this construction, the grating simply transmits the first light and diffracts the second light in the first and second lights whose polarizing directions cross perpendicularly. The second laser beam is formed by the diffracted light. At the time of the reproduction of information, consequently, the power of the second laser beam is reduced to a power at which the information which has already been recorded on the adjacent track is not erased, and the occurrence of the erasure or the like of the information can be prevented.
According to the fourth aspect of the invention, in the pickup device according to the first to third aspects of the invention, a first light emission end for emitting the first light of the light source and a second light emission end for emitting the second light are deviated with a predetermined distance.
According to this construction, since the first light and the second light are emitted from the deviated positions, the first laser beam and the second laser beam which are not overlapped are irradiated to each track. The increase in power to the track due to the overlap of the first and second laser beams is, thus, prevented and the erasure or the like of the information which has already been recorded on the track can be prevented at the time of the recording of information or reproduction of information.
According to the fifth aspect of the invention, in the pickup device according to the second to fourth aspects of the invention, a diffraction efficiency of the grating for the second light has been preset so that the second laser beam that is caused by the second light is set to a power at which the information on the track is not erased at the time of the reproduction of information.
According to this construction, the second laser beam which does not erase the information recorded on the track at the time of the reproduction of information is formed based on the power of the second light and the diffraction efficiency of the grating.
According to the sixth aspect of the invention, in the pickup device according to the first aspect of the invention, the light source is constructed by a separate structure comprising the first light source for emitting the first light and the second light source for emitting the second light, and the pickup device has: a grating for diffracting the second light; and wave synthesizing means for wave-synthesizing the diffraction light diffracted by the grating and the first light and irradiating the synthesized light to the information recording medium.
According to this construction, by adjusting the diffraction efficiency of the grating, it is possible to form the first and second laser beams of the powers such that the information which has already been recorded on the track is not erased [or the like] at the time of the recording of information or the reproduction of information. Each reflection light by the first and second laser beams is detected and the information whose crosstalk components have been suppressed can be reproduced on the basis of those detection results.
According to the seventh aspect of the invention, in the pickup device mentioned above, the first and second light sources further emit the first and second lights to the wave synthesizing means along the same optical axis.
According to this construction, the diffraction light in which the second light is diffracted by the grating, the 0th order light, and the first light are included in the wave synthesized light which is formed by the wave synthesizing means, the 0th order light and the first light are overlapped, and the first laser beam is caused. The diffraction light becomes the second laser beam. By controlling the powers of the first and second lights at the time of the recording of information or reproduction of information, therefore, the precise recording of information or reproduction of information can be performed. Since the power of the second laser beam is reduced in dependence on the diffraction efficiency of the grating, the erasure or the like of the information which has already been recorded is prevented and the reproduction of information can be performed. Each reflection light by the first and second laser beams is detected and the information whose crosstalk components have been suppressed can be reproduced based on those detection results.
According to the eighth aspect of the invention, in the pickup device according to the first to seventh aspects of the invention, the control means further controls so as to stop the emission of the second light or controls the second light so as to be set to a power at which the information recorded on the track is not erased at the time of the recording of information.
According to this construction, an erroneous erasure of the adjacent track due to the second light can be prevented at the time of the recording of information.
According to the ninth aspect of the invention, in the pickup device according to the first to eighth aspects of the invention, the control means further controls the second light so as to be set to a power at which the information recorded on the track is not erased at the time of the reproduction of information.
According to this construction, at the time of the reproduction of information, the tracking servo and focusing servo can be performed on the basis of the reflection light caused by the second light, and the information whose crosstalk components have been suppressed can be reproduced on the basis of each reflection light caused by the first and second lights.
According to the invention, there is provided an information recording/reproducing apparatus having the pickup device according to the first to ninth aspects of the invention, wherein the apparatus further comprises a crosstalk cancelling circuit for detecting each reflection light which is caused when the first and second laser beams are reflected by the track at the time of the reproduction of information and removing crosstalk components included in the reflection light caused by the first laser beam on the basis of each detection signal.
According to this construction, at the time of the recording of information or reproduction of information, the erasure or the like of the information which has already been recorded is prevented and, at the time of the reproduction of information, the crosstalk cancelling circuit reproduces the information whose crosstalk components have been suppressed on the basis of each reflection light caused by the first and second laser beams.